Combustible solid dispersions



United States Patent Oflice Patented Oct. 1, 1963 This invention relates to dispersions of combustible lids such as metals and the like. More particularly, is concerned with dispersions of certain metals having ixotropic properties. It is known that finely-divided metals such as magneim may be suspended in jet fuel and can be used for iproving combustion and imparting higher volumetric ergy levels in the after burners of jet engines. Because the density of the finely-divided metals other than tali metals and their higher melting points, it is dilficult obtain a suspension of the metal wherein the distriburn of the metal can be retained over extended periods time. When employing these dispersions for purposes are particularly given hereinafter, it is desirable that a metal or equivalents be uniformly distributed in hyocarbon oil for easy handling and that they be essenlly non-settling. While it is desirable to maintain iximum dispersion of the combustible solids in the hyocarbon medium, it is also desirable for many mechauns that the compositions be thixotropic so that they 1y be pumped and sprayed at will. It is an object of the present invention to improve disrsions of metals and the like. It is a particular object the invention to provide dispersions which are in the m of mobile slurries or gels having thixotropic prop- .ies. Another object is to provide novel metal disrsions having thixotropic properties which are stable settling, having uniform properties over a wide temrature range and do not settle at higher temperatures. ll further objects include the provision of novel sususions of metals ideally suited as fuels or additives for :ls for ram jet and turbo jet engines, and bipropellants missiles, rockets, flame throwers, and the like. Other iects will become apparent from the discussion hereiner. Now, in accordance with this invention, novel thixopic dispersions having the desirable properties of high isity fuels comprise suspensions of combustible solids a hydrocarbon base, the thixotropic properties being )VidBd by the presence of 0.25% by weight of a tal salt of a C alkyl monoester of a C alkylrcaptomethylphosphonic acid, the metal being at least a of the group consisting of groups III, IV and VIII the periodic system and having an atomic number ween l3 and 28. More particularly, the invention wides compositions having a major proportion of avdered metals, said metal being selected from lithium 1 groups II, III and IV of the periodic table and having mic numbers between 3 and 40, their hydrides, borides 1 mixtures thereof, the powdered metal being suslClEd in a normally liquid hydrocarbon and thickened form a thixotropic composition by means of the above ined metallic phosphonate salts. Special objectives are ained by the additional presence of wetting or dissing agents and oxidizing agents such as ammonium ate or ammonium perchlorate.

The metallic salts used as the thickening agent to provide thixotropic properties may be a basic or neutral metallic salt of phosphonate having the general configuration wherein R has from 4 to 18 carbon atoms and R is an alkyl radical having from 1 to 8 carbon atoms. The metals to be utilized in the salt formation are derived from groups III, IV and VIII of the periodic table and have atomic numbers from 13 to 28, the most favored metals being aluminum, iron, titanium, cobalt and nickel. Suitable species for the present purpose include the following:

Fe salt of monobutyl decylthiomethylphosphonate Al salt of monobutyl decylthiomethylphosphonate Ti salt of monohexyl dodecylthiomethyl phosphonate Co salt of monoethyl octadecylthiomethyl phosphonate Ni salt of monooctyl octylthiomethyl phosphonate The powdered metals are selected from metals including lithium and groups II, III and IV of the periodic table and include particularly beryllium, boron, magnesium, aluminum, and titanium. It is preferred that the particles of the powders be less than 200 microns in diameter and preferably between 0.1 and 1.0 micron on average. Mixtures of the metals may be used and mixtures of particle sizes may be employed for the purpose of providing more stable suspensions and suspensions having special properties. In the event that metals tend to react with the phosphonate salts and cause breaking or weakening of the thixotropic gel, the particles of the metal may be provided with superficial coating to isolate the metal such as resins, plastics or metal oxides. Alumina and perfiuoro carbons are examples of materials for this purpose.

Certain accelerators may be employed in conjunction with the powdered or flaked metals. Of these, high molecular weight fatty acid soaps of groups 111 and IV metals are preferred. Optimum results are obtained if the fatty acid has from 14 to 18 carbon atoms per molecule. Soaps of aluminum, magnesium, titanium, zirconium and tin are most efficient, particularly if they are the stearates, palmitates, oleates, or ricinoleates thereof. The term fatty acid is meant in this case, to include saturated fatty acids, unsaturated fatty acids and hydroxy fatty acids. Typical species for this purpose are the following:

Al stearate Mg palmitate Tin oleate Zirconium ricinoleates It is preferred that from about 0.1 to 5% by weight of the soap, based on the weight of the combustible solid, be employed for this purpose.

The three component essential composition of the invention therefore comprises the powdered combustible solid as described above, the hydrocarbon carrier and the phosphonate salt thixotropic gelling agent. Such compositions are particularly useful in the operation of ram jets which fly at altitudes where air provides sufficient oxygen for oxidation of the combustible particulate solid. Under other conditions it is possible to burn such com positions in conjunction with an oxidizing agent which may be injected separately or combined with the basic composition described above. For example, bipropellant systems comprise co-injection of the basic three component system described above with separate injection of an oxidizing agent such as liquid hydrogen peroxide, oxygen, and nitrogen tetroxide. Monopropellant systems are classified as those in which the oxidizing agent forms a component part of the fuel charge. In this case it is preferred that the oxidizing agent be added in the form of finely divided solid oxidizers, particularly ammonium or group I metal nitrates or perchlorates, e.g. ammonium perchlorate, amomnium nitrate, etc. Encapsulated components of any of the compositions discussed throughout this specification may be employed as well.

The preparation of the subject metallic salts of the phosphonates is described in copending patent application Serial No. 7,781, filed February 10, 1960.

In many cases it is desirable to provide thixotropic compositions containing the maximum. amount of particulate combustible solids possible. In this case it is often desirable to include dispersing agents, otherwise referred to as wetting agents, for the purpose of facilitating mobility and pumpability and maintaining the solid in thixotropic state while at the same time maximum solids content is achieved. A number of classes of dispersing agents are useful for this purpose such as the following:

DISPERSING AGENTS (1) Hydrocarbon-soluble hydrolyzed copolymers, formed by copolymerizing C straight-chain alpha olefins with -5 mols (per mole of olefin) of a vinyl ester, e.g. vinyl formate, vinyl acetate, vinyl butyrate or vinyl benzoate, mol 'wt. 400015,000. (2) Copolymers of (a) a mono-vinyl-substituted pyridine, (d) lauryl and stearyl methacrylate in a mol ratio between 1:4 and 4:1 and (c) a C alkyl acrylate, mol wt. 5x10 to 25x10. (3) Copolymers of (a) a vinyl pyridine, (b) (3 alkyl esters of acrylic or methacrylic acid, mol ratio 1:2 to 1:10, mol wt. 5X10 to 2.5x 10 (4) Sorbitan, glycol sorbitan, and polyoxyethylene sorbitan esters of C1448 fatty acids. (5) Polyoxyethylene esters of C1248 fatty acids. (6) High mol wt. fatty acids, esters or C fatty alcohols. Specific examples include:

Glycol sorb-itan laurate Polyoxyethylene sorbitan distearate Polyoxyethylene stearate Hexadecyl alcohol Copolymers of 2-methyl-5 vinylpyridine, stearyl methacrylate and lauryl methacrylate in 1:5:2.S mol ratio, 800,000 av. mol wt.

Copolymer of 1 mol hexadecene and 2.5 mols vinyl acetate, av. mol wt. 9,000.

Summarizing the above alternative compositions, the basic thixotripic composition is a three component one containing substantial amounts (90-25% by weight) of combustible solids, suspending proportions preferably 10-70% of a normally liquid hydrocarbon and 0.25-5% by weight of the metallic phosphonates providing thixotropic properties to the thickened compositions. If oxidizing agents are a fourth component of the above composition they are normally present in stoichiometric amounts relative to the combustible solids and hydrocarbon content and normally would be present in amounts between about 50 and about 80 parts by weight. Effective dispersing amounts of dispersion agents will vary from one composition to another, depending upon the specific dispersing agent and the specific solids to be dispersed thereby. This is usually between about 0.1% and about 5.0% by weight. The presence of water in an amount between about 0.1 and 0.5% is often effective in dispersing particulate metals in these compositions. Fuel catalysts such as the soaps are normally present in an amount between about 0.1 and 5% based upon the combustible solid.

The normally liquid hydrocarbon in which the combustible solids are to be suspended may be one or a mixture of hydrocarbons ranging from the gasolines through lubricating oils. For use in ram jets and the like it is preferred that fuels normally employed for jet propulsion be utilized. These are normally special hydrocarbon cuts in the kerosene boiling range but may include gas oils or higher boiling gasolines as well. Still higher volumetric thermal value is obtained by utilizing as the suspending fiuid highly saturated naphthenic materials such as decalins and alltylated decalins wherein the alkyl radicals have from 1 to 4 carbon atoms each. These may be modified by the presence of polycyclic hydrocarbons, preferably saturated, such as dimethanodecalins.

The following examples illustrate compositions according to the present invention.

Example I A kettle equipped with a high speed stirrer is used in the preparation of the following composition. Amorphous boron having an average particle size of about 1 micron diameter was dispersed by means of high speed stirring in 30 parts by weight of jet fuel meeting JP4 jet fuel specifications, 70 parts by weight of amorphous boron being so dispersed. The fuel was modified by the addition of l /2% by weight of the basic iron salt of monobutyl decylmercaptomethylphosphonate.

Example 11 A similar composition was prepared by dispersing powdered aluminum bearing a superficial coating of alumina in J P-4 jet hydrocarbon fuel, the thixotropic gelling agent being the aluminum salt of monobutyl decylmercaptomethylphosphonate.

Example 111 Magnesium powder having an average particle size of about 20 microns diameter is dispersed in a gas oil, the thixotropic agent being the iron salt of monoethyl dodecylmercaptomethylphosphonate. The composition contained 1% by weight of the phosphonate, 40% by weight of magnesium, the balance being gas oil.

Example IV High energy fuel compositions are provided by the combination of 70% zirconium decaboride, 1% of the aluminum salt of mono-octyl octylmercaptomethylphosphonate suspended in 29% by Weight of a mixture of decalins.

Example V A mono-propellant composition is provided by the suspension of 30% decaborane and 40% ammonium perchlorate in 28% of kerosene hydrocarbons, the dispersion being aided by the presence of 1% by weight of a copolymer of 2-rnethyl-S-vinylpyridine, stearyl methacrylate and lauryl methacrylate in 1:5:2.5 mol ratio having an average molecular weight of about 800,000. The thixotropic gelling agent for this composition is 1% by weight of the titanium salt of monohexyl octadecylmereaptomethylphosphonate.

We claim as our invention:

1. A thixotropic composition consisting essentially of a major proportion of finely divided aluminum dispersed in a normally liquid hydrocarbon and as a suspending agent for the aluminum 0.252.5% by weight of the basic iron salt of monobutyl decylmercaptome-thylphosphonate.

2. A thixotropic composition comprising from 25 to percent by weight of a finely divided combustible solid of the group consisting of lithium and metals of groups II, III and IV of the periodic table having atomic numbers between 4 and 50, their hydrides, borides and mixlres thereof, suspended in from about 10 to about 70 peram by weight of a normally liquid hydrocarbon and, as a lickening agent for said solids from about 0.25 to 5 per- :nt of weight of an aluminum salt of a C alkyl mono ;ter of a C1043 alkylmercaptomethylphosphonic acid.

3. A composition according to claim 2 wherein the parcles of aluminum bear a superficial coating of alumina. 4. A thixotropic composition comprising from 25 to by weight of a finely divided combustible solid of re group consisting of lithium and metals of groups II, I and IV of the periodic table having atomic numbers atween 4 and 50, their hydrides, borides and mixtures lereof, suspended in a normally liquid hydrocarbon and, a a thickening agent for said solid, an iron salt of a alkyl monoester of a C alkylmercaptomethylhosphonic acid.

5. A composition according to claim 4 wherein the lItlClCS of finely divided combustible solid bear a super- :ial coating of a polyvalent metal oxide.

6. A composition according to claim 4 containing in ldition 0.l5% by weight, based on the combustible Ilid, of a higher fatty acid soap of a group IIIV metal. 7. A composition according to claim 4 containing in ldition a minor dispersion improving amount, based 1 the combustible solid, of a dispersion agent.

8. A composition consisting essentially of the following )mponents in the stated proportions:

Percent by weight inely divided boron 2575 eroscne 2570 on salt of mono-butyl decylmercaptomcthylphosphonate 0.5-2.5 'ater 0.1-0.5

9. A thixotropic composition comprising from 25 to by weight of a finely divided combustible solid selected from the group consisting of lithium, and metals of groups II, III and IV of the periodic table having atomic numbers between 4 and 50, their hydrides, borides and mixtures thereof, suspended in a normally liquid hydrocarbon and, as a thickening agent for said solid, a metal salt of a phosphonatc having the general configuration RSClli 0 P R1-o \OII wherein R is an alkyl hydrocarbon having from 4 to 18 carbon atoms and R is an alkyl radical having from 1 to 8 carbon atoms, said metal being at least one of the members selected from the group consisting of groups ill, IV, and VIII of the periodic system and having an atomic number between 13 and 28.

10. A composition according to claim 4 wherein the iron salt is a basic salt.

11. A composition according to claim 4 containing a solid oxidizing agent selected from the group consisting of ammonium and group I metal nitrates and perchlorates.

References Cited in the file of this patent UNITED STATES PATENTS 2,311,306 Ritchey Feb. 16, 1943 2,873,178 Biswell Feb. 10, 1959 2,927,849 Greblick et a1 Mar. 8, 1960 2,954,284 Toulmin Sept. 27, 1960 2,971,097 Corbett Feb. 7, 1961 2,991,244 Pattendcn et a1. July 4, 1961 

9. A THIXOTROPIC COMPOSITION COMPRISING FROM 25 TO 90% BY WEIGHT OF A FINELY DIVIDED COMBUSTIBLE SOLID SELECTED FROM THE GROUP CONSISTING OF LIGHIUM, AND METALS OF GROUPS II, III AND IV OF THE PERIODIC TABLE HAVING ATOMIC NUMBERS BETWEEN 4 AND 50, THEIR HYDRIDES, BORIDES AND MIXTURES THEREOF, SUSPENDED IN A NORMALLY LIQUID HYDROCARBON AND, AS A THICKENING AGENT FOR SAID SOLID, A METAL SALT OF A PHOSPHONATE HAVING THE GENERAL CONFIGURATION 